The present invention relates to implantable medical devices, and more particularly to a method and apparatus for detecting a power link between an external programmer/controller device and an implantable medical device.
In U.S. Pat. No. 5,569,307 there is disclosed an implantable cochlear stimulator (ICS) having back telemetry features. The back telemetry features allow an external wearable processor (WP), inductively linked with the ICS, to receive data and status signals from the ICS. These data and status signals assure that the WP is in proper signal contact with the ICS, and that the ICS is functioning properly. More particularly, as disclosed in the '307 patent, only when a prescribed combination of various status signals within the ICS are present, is a back-telemetry carrier signal and FSK data transmitted to the WP. The back-telemetry carrier signal, when received at the WP, thus acts as a handshake signal to signal the WP that the ICS is in proper signal communication with the WP, and that operation of the ICS can proceed. If the backtelemetry carrier signal is not received by the WP, then the WP does not send the necessary initialization data to the ICS, and operation of the ICS cannot proceed. The '307 patent is incorporated herein by reference.
Unfortunately, detection of the back-telemetry power signal requires appropriate detection circuitry within the external unit. While such detection circuitry may be of any straightforward design, it takes additional components and consumes additional power. Additional componentry and higher power consumption were not significant design considerations for a WP of the type disclosed in the '307 patent because the WP therein disclosed is a belt-worn or pocket-carried device powered with an easy-to-replace battery. However, such is not the case with the newer external units designed to be worn behind the ear. Rather, such behind-the-ear (BTE) units must be both physically small and light weight. Moreover, such BTE units, while ultimately designed, perhaps, for use with more-efficient implantable units, must be backwards compatible. That is, the small, light-weight BTE unit must still provide the operating power and control signals necessary to operate an existing ICS, including an ICS of the type described in the '307 patent. Hence, it is seen that there is a need for power-link detection circuitry within the BTE unit that is able to detect when a valid power link exists between the BTE and the ICS. Such power-link detection circuitry must be much smaller than, and must consume significantly less power than, the detection circuitry that would otherwise have to used to detect a back-telemetry carrier signal.